The overall objective of the research of program is the clarification of trigeminal nociceptive mechanisms, especially in the brainstem, related to acute and chronic pain conditions that afflict the face and mouth. Our recent NIH-supported studies, which have produced 10 papers and 7 abstracts in 1981 and 1982, have helped provide some of the insights into the brainstem mechanisms involved in dental and facial pain in particular. Major gaps or uncertainties in our knowledge however still exist in the neural mechanisms underlying dental, joint and muscle pain especially and in the processes associated with pain conditions that may be related to muscle dysfunction (e.g. TMJ or myofascial pain dysfunction syndrome) or to sensory loss (e.g. painful sensory neuropathies, neuralgias, causalgias). We will use our expertise and experience gained over the last 18 years with the trigeminal system of the cat and monkey and continue to examine functionally identified single noticeptive and nonnociceptive neurons recorded electrophysiologically in the trigeminal spinal tract nucleus of the cat. In particular, we now propose to determine which types of neurons relay joint and musle nociceptive information and to study the response properties and convergent patterns seen in these neurons with stimulation of muscle, joint and other orofacial afferents (Aim i); to determine if these responses can be modulated by other sensory inputs and by descending influences from brainstem, cortex and thalamic sites implicated in pain and analgesia and gain insights into the underlying neurochemical mechanisms by studying the effects on the modulatory influences of antagonists to the possible neurochemicals involved (Aim ii); and continue to investigate the effects of sensory loss on the functional organization of these neurons by delineating further the changes in their functional properties that we have shown to occur with tooth pulp extirpation and comparing them with likely changes that may be induced by deafferentation of other orofacial structures or interruption of the modulatory interaction that has been demonstrated between different components of the nucleus (Aim iii). We anticipate that our findings will lead to future studies in kittens and chronic recording investigations in adult animals to examine maturational and behavioral changes that may be associated with orofacial sensory alterations.